The present invention relates to machine tools and other types of machines in general, and more particularly to improvements in apparatus for monitoring various parameters of workpieces in machine tools, especially in plain grinding machines. Still more particularly, the invention relates to improvements in apparatus of the type wherein the diameter of a workpiece which is held in a predetermined position is monitored by a system employing two sensors at least one of which is movable with reference to the other sensor so that the two sensors can engage a round or partially round workpiece at two points which are disposed diametrically opposite each other with reference to the axis of the workpiece.
It is customary to equip numerous types of machine tools, for example, plain grinding machines, with gauges which are used to monitor the diameter as well as the axial position of a workpiece. Such gauges are practically indispensable in machine tools which must treat workpieces with a high or very high degree of precision. The diameter gauge monitors the diameter of a workpiece before, during and/or subsequent to completion of material removal, and the gauge which ascertains the axial position of a workpiece is or can be put to use prior to start of material removal so as to ensure that the workpiece will be held in an optimum axial position with reference to the material removing tool or tools, e.g., with reference to one or more rotary grinding wheels in a plain or other grinding machine. Certain gauges which are used to ascertain the axial position of a workpiece in a plain grinding machine are called length measuring gauges; however, such definition is actually a misnomer because the gauge does not ascertain the length but rather the axial position of the monitored workpiece. In order to facilitate accurate selection of the axial position of a round workpiece, e.g., an elongated cylindrical shaft, such a workpiece is often provided with an annular shoulder adapted to be engaged by a component of the gauge which monitors the axial position of the workpieces; electric signals or other indications which are furnished by such gauge are used to correct, if necessary, the axial position of the monitored workpiece. For example, when the gauge which monitors the axial position of a workpiece in a plain grinding machine is in engagement with the aforementioned shoulder, the carriage which can move the workpiece in the axial direction is shifted until the indication which is furnished by the gauge denotes that the actual axial position of the workpiece matches the desired or optimum axial position or that the difference between the actual and desired axial positions is negligible or within the range of acceptable deviations from an optimum axial position. It is also possible to use the signals which are furnished by the just discussed gauge for monitoring the axial position of a workpiece as a means for changing the position of the material removing tool with reference to the workpiece until the tool and the workpiece assume optimum positions relative to each other. For example, signals which are generated by a diameter monitoring gauge or by a gauge which monitors the axial position of a workpiece can be transmitted to the numerical controls of a plain grinding machine. Still further, signals which the gauges transmit to the controls of a machine tool can be used to compensate for deviations from an optimum diameter or from an optimum axial position in a different way.
A drawback of presently known apparatus which employ the just discussed gauges is that they are complex, bulky and expensive. Thus, if such gauges are used to transmit signals to the automatic controls of a machine tool, it is necessary to provide an operative connection between the controls and each of the gauges and it is further necessary to provide a drive for at least one sensor of each of these gauges. All this contributes to the cost as well as to space requirements of conventional apparatus so that the workpiece is not readily accessible since the gauges cannot be placed at a substantial distance from the material removing station unless the machine is further equipped with means for moving the gauges toward and away from engagement with the workpiece.